1. Field of the Invention
The invention concerns a membrane separation process for the enrichment of at least one gas component in a gas flow, particularly for the oxygen enrichment of the air and/or for the enrichment of carbon dioxide in a gas flow. The gas flow for enrichment of the gas is led to a membrane separation unit including at least one membrane. This is where the separation of the gas flow into a retentate, which is discharged on the retentate side of the membrane, and a permeate, which is discharged on the permeate side of the membrane, takes place. Secondly, this invention relates to a membrane-separation plant for the enrichment of at least one gas component in a gas flow, particularly for the oxygen enrichment of air. It provides at least one membrane separation device including at least one membrane, with the gas flow supposed to the enrichment of the gas being led to a membrane separation unit. The separation of the gas flow into a retentate, which is discharged on the retentate side of the membrane, and a permeate, which is discharged on the permeate side of the membrane, takes place on the membrane.
2. Description of Related Art
Today oxygen and nitrogen are mainly generated by means of the cryogenic separation developed by Linde and Claude 100 years ago (Air Liquide), which presupposes that air is cooled down to −180° C. and then is distilled and/or rectified. Because of the extreme low temperatures, energy consumption costs are inevitably high. The separation device industry concerned with the separation of technical gas are extremely expensive because of their complex form and arrangement. They are used for the production of pure gases in large volumes.
Further possibilities to produce oxygen-enriched air are the methods of adsorptive decomposition into nitrogen and oxygen using the molecular sieve, zeolites and activated charcoal. Separation takes place according to the size of molecules, as well as to the adsorptive and diffuse interactions. The disadvantages of the aforesaid method are high energy consumption and expensive equipment. The plants are usually built for the industry with the purpose to provide with high productivity, primarily for the pure gases. Because of the complexity of the components the costs for investment, capital and maintenance are very high.
In comparison to the existing gas separation methods, the gas separation by membrane is remarkable for its low technical expense. Speaking about the membranous gas separation, it is relevant to distinguish “fluid” or “gaseous” according to the aggregative state, and, according to the mediums or components to separate gas-membrane contactor, membranous pervaporation and gas permeation. The methods using the gas-membrane contactors are characterized by the fluid phase on the permeate side of the membrane, where the permeate is absorbed and the chemical reaction takes place. The gas pervaporation is a method for the separation of organic water solutions or of organic fluids, allowing the permeated components to go from the liquid state into the vaporized state. The distinguishing feature of the gas permeation is that both the feed stream, respectively the retentate stream as well as the permeate stream, are in gaseous state.
The advantage of the gas separation by means of membranes is the low-energy generation of gas of the desired quality. The costs for providing the device as well as for maintenance and service are considerably lower compared to the classical separation methods. Furthermore, the control and regulation expenses for the present membrane separation process are low. The facilities are often modularly built and enable the precise adjustment and regulation of the necessary volume streams. Another advantage is the efficiency of the equipment and the specific lifespan of the single components. One disadvantage of the existing methods for membrane separation is that the gas must be led to the membrane separation unit under high pressure to allow the permeation of the component to be separated, respectively enriched, to pass into the permeate stream. The compression of the input gas flow before entering the membrane separation unit involves considerable energy consumption and is therefore very expensive.